Difference between revisions of "DSP"

Bit 14 is used as End-Of-List marker.

DSP address interleave (Bit-offset 0; 1-bit):

• 0 = Addressing using:

  for (sample_index = 0; sample_index < sample_count; sample_index++) {
    transfer_dsp_word(dsp_address + sample_index * dsp_step_size)
  }

• 1 = Addressing using:

  for (block_index = 0; block_index < block_count; block_index++) {
    for (channel_index = 0; channel_index < channel_count; channel_index++) {
      transfer_dsp_word(dsp_address + block_index + channel_index * dsp_step_size)
    }
  }

Direction (Bit-offset 1; 1-bit):

• 0 = Buffer to DSP (In)
• 1 = DSP to buffer (Out)

Unknown (Bit-offset 2; 2-bits):

• 0 = ?
• 1 = ?
• 2 = ?
• 3 = ?

Buffer offset writeback (Bit-offset 4; 1-bit): Only used for scratch buffers, behaves like 0 otherwise.^[FIXME]

• 0 = Don't update buffer offset (Word 4)
• 1 = Update buffer offset (Word 4); this respects address wrapping of circular buffers

Buffer (Bit-offset 5; 4-bits):

• 0x0 = FIFO0 (In / Out)
• 0x1 = FIFO1 (In / Out)
• 0x2 = FIFO2 (Out only; Buffer to DSP is ignored)
• 0x3 = FIFO3 (Out only; Buffer to DSP is ignored)
• 0x4 = ?
• 0x5 = ?
• 0x6 = ?
• 0x7 = ?
• 0x8 = ?
• 0x9 = ?
• 0xA = ?
• 0xB = ?
• 0xC = ?
• 0xD = ?
• 0xE = Scratch (Circular)
• 0xF = Scratch

Unknown (Bit-offset 9; 1-bit):

• 0 = ?
• 1 = ?

Sample format (Bit-offset 10; 3-bits): [FIXME]

• 0x0 = 8 bit (1 DSP word / 1 byte); sample-count must be multiple of 4, or transfer is skipped; rounded; byte MSB is flipped
  • Buffer to DSP: bytes: 0x12,0x34,0x56,0x78 → words: 0x920000, 0xB40000, 0xD60000, 0xF80000
  • Buffer to DSP: bytes: 0x92,0xB4,0xD6,0xF8 → words: 0x120000, 0x340000, 0x560000, 0x780000
  • DSP to buffer: words: 0x927FFF, 0xB47FFF, 0xD67FFF, 0xF87FFF → bytes: 0x12,0x34,0x56,0x78 (Rounded down)
  • DSP to buffer: words: 0x928000, 0xB48000, 0xD68000, 0xF88000 → bytes: 0x13,0x35,0x57,0x79 (Rounded up)
  • DSP to buffer: words: 0x800000, 0x7E7FFF, 0x7E8000, 0x7FFFFF → bytes: 0x00,0xFE,0xFF,0xFF (Saturated)
• 0x1 = 16 bit (1 DSP word / 2 bytes) sample-count must be multiple of 2, or transfer is skipped; truncated
  • Buffer to DSP: bytes: 0x34,0x12 → word: 0x123400
  • DSP to buffer: word: 0x1234FF → bytes: 0x34,0x12 (Truncated)
  • DSP to buffer: word: 0x123400 → bytes: 0x34,0x12 (Truncated)
• 0x2 = 24 bit in MSB (1 DSP word / 4 bytes); padded
  • Buffer to DSP: bytes: 0x00,0x56,0x34,0x12 → word: 0x123456 (Padding ignored)
  • Buffer to DSP: bytes: 0xFF,0x56,0x34,0x12 → word: 0x123456 (Padding ignored)
  • DSP to buffer: word: 0x123456 → bytes: 0x00,0x56,0x34,0x12 (Zero padding)
• 0x3 = 32 bit (2 DSP words / 4 bytes); trunacted
  • Buffer to DSP: bytes: 0x12,0xBC,0x9A,0x78 → words: 0x120000, 0x789ABC
  • DSP to buffer: words: 0x12FFFF, 0x789ABC → bytes: 0x12,0xBC,0x9A,0x78 (Truncated)
  • DSP to buffer: words: 0x120000, 0x789ABC → bytes: 0x12,0xBC,0x9A,0x78 (Truncated)
• 0x4 = Transfer skipped
• 0x5 = Transfer skipped
• 0x6 = 24 bit in LSB (1 DSP word / 4 bytes); padded
  • Buffer to DSP: bytes: 0x56,0x34,0x12,0x00 → word: 0x123456 (Padding ignored)
  • Buffer to DSP: bytes: 0x56,0x34,0x12,0xFF → word: 0x123456 (Padding ignored)
  • DSP to buffer: word: 0x123456 → bytes: 0x56,0x34,0x12,0x00 (Zero padding)
• 0x7 = Transfer skipped

Unknown (Bit-offset 13; 1-bit):

• 0 = ?
• 1 = ?

DSP address step size (Bit-offset 14; 10-bits):

Used in DSP address calculation

• Non-interleaved mode:

Sample count (Bit-offset 0; 24-bits):

The number of samples to be transferred

• Interleaved mode:

Channel count (Bit-offset 0; 4-bits):

The number of channels minus 1. For 3 channels, this has to be 0x2.

Block count (Bit-offset 4; 20-bits):

The number of blocks to be transferred.

• 0x0000 - 0x17FF = X-Memory
• 0x1800 - 0x27FF = Y-Memory
• 0x2800 - 0x37FF = P-Memory

This is the offset within the buffer where the first sample is accessed.

If this is above or equal to the buffer end (buffer base + buffer size), then the write will behave like a non circular write.

The start address of the buffer.

Size of buffer minus 1. For a buffer with 0x1000 bytes, this has to be 0xFFF.